DIAGNOSIS The most likely cause is a failed heating element. The second is a blown thermal fuse that protects it.
FIX Run a diagnostic test. Press and hold the Cycle Select and Start buttons for 3 seconds. The display will show test codes. Let it run through its tests. It will flash an error code if it detects an open heating element or thermal fuse.
IF THAT DIDN'T WORK If no error code appears, the heating element may still be bad. Unplug the unit. Remove the lower access panel. The heating element is a looped metal rod at the bottom of the tub. Use a multimeter to check for continuity. If it reads OL (open loop), it's dead.
HEADS UP The heating element also heats water during wash cycles. If it's dead, your dishes won't get clean either due to low water temperature.